[FLINK-30284][flink-metrics] Modify configuration of DataDog http reporter url.

[Wosin]

What is the purpose of the change

This change removes the dataCenter configuration for DataDog reporter and replaces it with dataCenterUrl that allows users to configure whole address of the data center to use.

Brief change log

• Remove dataCenter key from DataDog reporter configuration.
• Add new configuration option dataCenterUrl that accepts full address of Data Dog site, it defaults to US data center.

Verifying this change

Please make sure both new and modified tests in this PR follows the conventions defined in our code quality guide: https://flink.apache.org/contributing/code-style-and-quality-common.html#testing

(Please pick either of the following options) This change is already covered by existing tests, such as DatadogHttpClientTest.

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): no
• The public API, i.e., is any changed class annotated with @Public(Evolving): no
• The serializers: no
• The runtime per-record code paths (performance sensitive): no
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: no
• The S3 file system connector: no

Documentation

• Does this pull request introduce a new feature? no
• If yes, how is the feature documented? docs

[flinkbot]

CI report:

• 4c2cc92a9246f79e0edd28abeba74cfc61f339b5 Azure: FAILURE

Bot commands

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• @flinkbot run azure re-run the last Azure build

[anleib]

@Wosin can you please fix formatting. Would like to push this for a merge; my org recently migrated to US3 and broke all Flink metrics/dashboards/alerts.